d-d Excitations in Bilayer Manganites Probed by Resonant Inelastic X-ray Scattering

TL;DR

This study uses resonant inelastic x-ray scattering to investigate d-d excitations in bilayer manganites, revealing their non-local nature and dependence on magnetic order and wave vector, advancing understanding of electronic excitations in these materials.

Contribution

It provides detailed momentum and temperature dependence of d-d excitations in bilayer manganites, demonstrating their non-local character and magnetic coupling effects, which were not previously characterized in such detail.

Findings

Observed dispersion of d-d excitations up to 0.5 eV.

Identified strong dependence of excitation intensity on wave vector and temperature.

Confirmed the intersite charge transfer nature of the excitations.

Abstract

We report a high resolution resonant inelastic x-ray scattering investigation of the bilayer manganites La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ with $x = 0.36$ and $0.5$. The momentum dependence along the crystallographic $(110)$ direction for energy losses $1\,\rm{eV} \leq \Delta E \leq 15\,\rm{eV}$ has been measured in detail with the data analysis focusing on the energy loss region $1\,\rm{eV} \leq \Delta E \leq 5\,\rm{eV}$, which includes a strong peak located at $\Delta E \approx 2\,\rm{eV}$. We observe a clear dispersion of up to $0.5\,\rm{eV}$ in the measured $\textbf{q}$ range, which is direct evidence of the non-local character of this excitation. Further, we found that the intensity in this low energy region strongly depends on both the reduced wave vector $\textbf{q} = (h, h, 0)$, $h = 0.1 - 0.5$, and temperature, i.e. different ordered phases. Results can be explained via an intersite $d-d$ charge transfer excitation, proposed for pseudo-cubic manganites, where the hopping rate is strongly increased (decreased) by ferromagnetic (antiferromagnetic) alignment of neighboring in-plane Mn ion core spins.